1. Field of the Invention
The present invention relates to a voltage generating circuit and a control method thereof.
2. Description of the Related Art
In a nonvolatile memory such as a flash memory, a high voltage of ±16 V or more is necessary to perform write operations and erase operations in its memory cell. For this reason, a conventional nonvolatile memory is equipped with a voltage generating circuit which raises a power supply voltage of, for example, 1.8 V to 3 V in order to generate a high voltage in the memory chip.
Unexamined Japanese Patent Publication No. 2002-26254 discloses a semiconductor integrated circuit including a nonvolatile memory having the aforementioned voltage generating circuit. In this semiconductor integrated circuit, a charge pump in which the voltage generating circuit carries out a first stage voltage pumping based on a power supply voltage is connected in parallel in terms of the capacity while a charge pump which carries out a second stage voltage pumping based on the voltage raised by the aforementioned charge pump is connected in series in terms of the capacity.
In the above-described semiconductor integrated circuit, if the first stage voltage pumping is carried out by the capacity parallel connection type charge pump, the charged electricity is accumulated in parasitic capacity even if the quantity of connection stages of the capacity component is increased (distinguishable from a case of carrying out the first stage voltage pumping by a capacity series connection type charge pump), thereby causing no such inconvenience that a raised voltage is saturated.
Further, in the above-described semiconductor integrated circuit, even if the second stage voltage pumping is carried out by the capacity series connection type charge pump, the voltages applied to the capacity component of each of the stages connected in series become substantially equal, thereby facilitating pressure resistant design. Therefore, the above-described semiconductor integrated circuit causes no inconvenience as described above compared with a case of carrying out the first stage voltage pumping by the capacity series connection type charge pump while carrying out the second stage voltage pumping by the capacity parallel connection type charge pump. Thus, the semiconductor integrated circuit can raise the voltage of a power supply effectively so as to generate a high voltage.